The broad purpose of the proposed project is to learn how much electrophysiologic information can be extracted from potentials recorded at locations outside of the heart. In essence, a variety of solutions to the so-called inverse electrocardiographic problem will be sought. These will include representation of cardiac behavior in the form of 1) an equivalent dipole-multipole series, extending through the hexadecapolar approximation, 2) a mobile dipole whose strength, orientation, and location vary as functions of time, 3) two such mobile dipoles, 4) a moving dipole together with an independently locatable quadripole, and 5) multiple dipole reconstructions. Due to the exacting quantitative demands of the project, recording procedures will be performed on isolated amphibian and mammalian hearts in an accurately fabricated "artificial torso" with precisely determinable transfer coefficients between the biologic generator and the volume conductor surface. Advanced signal processing and data reduction methods will also be required. Apart from the search for intrinsic electrophysiologic information, the proposed technique itself amounts to a precisely defined form of quantitative electrocardiography which should prove useful in evaluating a variety of interventions. A particularly exciting prospect is the possibility that it will eventually be feasible to compare realistic generator configurations, inversely determined from externally recorded data, with information obtained from the same hearts by direct epicardial and intramyocardial registration.